Electric machines, such as induction machines, switched reluctance machines, and other comparable types of electric machines, are commonly used in the industry to convert electrical energy into rotational torque or rotational torque into electrical energy for any one of a variety of different applications including machine tools, traction motors, industrial work machines, stationary drive machines, mobile work vehicles, hybrid electric vehicles, and the like. Electric machines are commonly employed in association with a primary power source, such as an internal combustion engine or any other comparable prime mover, to provide a combined genset which serves to generate electrical and/or mechanical energy.
In a variable speed genset, a primary power source is mechanically and/or rotatably coupled to a rotor of the electric machine, while the stator of the electric machine is in turn electrically coupled to a common bus of the associated vehicle, machine, or tool. The common bus generally communicates electrical power between the electric machine and one or more connected loads. In a generating mode of operation, the primary power source rotates the rotor of the electric machine to cause electromagnetic interactions which generate electrical energy to be employed by one or more of the connected loads. Moreover, in typical variable speed gensets, the operating speed of the primary power source may be varied according to the load demand, as shown, for example, in FIG. 1. For instance, in order to accommodate an increase in load demand, the engine speed can be increased to increase the electrical power produced by the electric machine. Alternately, if the load demand is reduced, the engine speed can be decreased to conserve fuel.
During transient or step load conditions when the primary power source (for example, an engine) speeds are relatively low, the power output by the genset at such low speeds may be insufficient to maintain desirable operation of each connected load. Accordingly, traditional gensets may also employ an energy storage device such as a battery, an ultracapacitor, or the like. The discharge of such an energy storage device may be converted by a nominal boost converter to substantially match the bus voltage of the common bus. The additional energy supplied by the energy storage device may then be applied to the bus voltage to assist the electric machine in supporting the connected loads. Alternatively, the speed of the primary power source may be kept artificially high in anticipation of transient or step loads. Such an arrangement may not provide optimal fuel efficiency.
U.S. Publication Number 2005/0063117, filed Nov. 5, 2004, (the '117 Application) relates to a power supply system for supplying electric power to various electrical equipment. The '117 Application describes a power supply system including a power control unit for controlling electric power supplied to a load, a battery condition sensing means for sensing the operative condition of the battery, and a load condition sensing means for sensing the operative condition of the electric load. In the power supply system, the variation of the power supply voltage at the time of the operative requirement of the electric load is estimated based on the condition of the battery and the electric load. Current supplied to electric loads is selectively limited when the estimated electric power supple voltage is smaller than a predetermined value. Although the '117 Application may describe a methodology for limiting current to loads, the '117 Application does not disclose a system or method for utilizing battery health for optimizing the speed of a power source to meet load demands.